Typically, the use of a beam of light as a detection tool for various objects is based on either measuring reflection or transmission of the detection beam by way of a photo sensor. The effectiveness of such methods depends largely on the optical qualities of the object in question; some objects are most effectively detected by way of reflection-based detection while other objects are most effectively detected using transmission-based detection.
Applications involving multiple objects in which each object has a different optical characteristics generally require multiple photodetectors